The answer is to use one of the options below to find the ESRIUK Product Licence Manager which allows you to register/update your licence file for Productivity Suite.

a. There should be a shortcut for the ESRIUK Product Licence Manager within the Programs list from the Start menu, but if it's not available then it may be necessary to install the latest Service Pack for the product. Go to http://www.esriuk.com/software/arcgis/productivitysuite/download to download the latest Service Pack for your version. After installation, the Licence Manager should then appear in the Programs list from the Start menu (depending on your Windows account/configuration).

b. The Licence Manager application can be found under C:\Program Files ¦ Program Files (x86) \ESRIUK\ProductivitySuite\bin\PSLicenceManager.exe

c. Launch ArcMap or ArcCatalog and go to Productivity > About ProductivitySuite..., click on View Licences in the bottom left corner and your Licence Manager will appear (Please make sure that Productivity Suite is enabled as an extension first. Go to Tools (for 9.x) /Customize (for v10) > Extensions and tick Productivity Suite on the list).

Launch the Licence Manager using any of the options above. Click on Import Licence and navigate to the xml licence file. After accepting the Licence agreement, your application is registered and ready to use.